Each one should be placed in the same place the first time.
There is refers here the
Know
... So they can see behind them and in front of
them at the same time. Squid and crabs have their eyes on stalks which can move.
Their field of vision is 360 degrees.
Human beings have a field of vision of only 180 degrees. But what our two eyes
see overlaps, so we have three-dimensional vision. We can see depth
and movement more accurately than most other animals. And that's what today's
program is about. Our eyes, how we see and how we use our eyes to learn about the
world around us.
Our eyes are incredible machines. We may not have the infrared vision of six
million dollar man, but we can see the smallest detail in a landscape full of
objects because their eyes are 3D. We can watch rapid movement and keep their eyes
in focus. And we've developed a sense of color and that helps us see shapes. But
the thing that allows all this to happen is light. Our world only comes to us
through our eyes because light shines on all the things that we see. And the major
source of light is the Sun.
I'd like to sing you a song. Sing about the morning sun.
I'd like to sing you a song. Sing about the morning sun.
Birds sing the glory of the sun in the early morning. Flowers and trees do the
same when they see it coming. Sun rises in the sky.
Shines on us all day long. In the morning, when I see it.
In the morning, it makes my life so sweet.
The colors of the new day look so fine in the early morning.
Fields of green dewdrops start to shine when they feel it coming.
Light is all around. So much now to see. In the morning, when I see it.
Most of our light comes from the Sun. Even at night we can still see by
sunlight because moonlight is light reflected from the Sun. Even on the
darkest night there is still sunlight for us to see by. The stars we see are
other Suns and lights from those other Suns helps to brighten up our night sky.
Of course we don't rely on natural light, light from the Sun, Moon and stars to
help us see. Ever since the Stern Age man has used fire to provide light and later
generations have used candles, gas, kerosene and nowadays we use electricity
to help us see. Whether the light we see by is provided by the Sun, Moon or Stars
or by electricity, all living things need eyes to see and if you look around you
at the people that you meet you'll notice that everyone's eyes are just a
little different from all the others.
All eyes react to light in the same way. In this case light from the Sun hits a
particular object, an ice cream cone, and is reflected towards the eye. It first
passes through the cornea, the clear transparent surface of the eyeball. Next
the light passes through the pupil, that black dot in the middle, which is not
really a dot at all but a hole. The pupil is surrounded by the iris, the coloured
part of your eye and we'll see in a moment how the iris is capable of
opening and closing the pupil. Behind the pupil is the lens. The lens focuses the
light and projects a clear image onto the retina, a kind of screen at the back
of the eye. This image is upside down. The brain is not only able to turn the image
right side up, it also recognises it and names it. In this situation when the
light from the Sun is very bright the pupil would be very small. The iris would
have closed around it, protecting the retina from an overabundance of light. On
the other hand if the light is very dim then the iris opens up. The larger pupil
lets larger amounts of light through to the retina and the eye can still see in
the dim light. If the amount of light is increased the iris closes around the
pupil making it smaller and protecting the retina. If the amount of light is
reduced the iris allows the pupil to grow larger, letting more light through
to the retina.
So when the amount of light increases the pupil becomes smaller and when the
amount of light decreases the pupil becomes larger. The light passing through
the pupil and falling on the retina sets off special detectors which send
electrical impulses to the brain. These detectors are called rods. There are 125
million rods in the retina. The rods around the edge of the retina are
especially sensitive to the movement of light and this explains why you can
notice movement out of the corner of your eye. In the more sensitive central
part of the retina there are a number of structures called cones along with the
rods and these enable us to see color. Certain cones can detect certain colors.
Some are sensitive to a kind of red, some to a blue-green, others to yellow. In some
people some types of cones are absent or incorrectly formed and we call them
colorblind. That doesn't mean that they can't see colors, it just means they
have trouble distinguishing between red and green or green and yellow and so on.
People with red and green blindness would have trouble picking out our
portrait of the cat. Let's make him clearer. If you're watching this program
in monochrome or black and white you obviously can't see the colors at all
but you're probably seeing the program the way animals see the world in terms
of light and shade. No one is yet certain whether or not animals can see color.
It's so difficult to research. The only creatures we're sure about are crabs and
it appears they don't see color at all. They must miss out a lot of the color on
the beach and in the water that we enjoy.
Reptiles on the other hand see color quite well, especially crocodiles.
Perhaps this lizard chose the pink flower because of its color. Most human
beings have a good sense of color and we need it. We use it all the time to
survive in the world around us.
At birth we come into a blurred world. A newborn baby can see light but he can't
distinguish any objects around him. Human babies open their eyes as soon as
they're born but it's several months before their eyes are properly able to
focus. Puppies and kittens have their eyes closed for the first few weeks of
their lives. They have to learn to move about by using their other senses
especially hearing and smell.
Human babies use a combination of senses to gradually learn about the world
around them and how to move in it to crawl to walk and run. The children of
four and five still do a lot of falling over because their eyes are still
developing and growing. Our eyes don't stop growing until we're about nine
years old and they don't settle down completely until the age of 12.
Meanwhile every time you wink or blink a liquid called tear film is washing your
eyes and protecting them. Even while you're asleep it's building up and
making sleep in the corner of your eyes.
This little girl doesn't have any problems with tear film but then she
doesn't have any tears either. Hey I bet you didn't know that tiny babies can't
cry. Oh they make lots of noise but their tear glands aren't yet developed
enough to let the tears roll down. I bet you've seen it lots of times. Making enough
noise to wake the neighbors two streets away and not a tear. Sometimes tear goes
down into the baby's nose and makes him sneeze. I bet you have noticed that tiny
babies sneeze a lot so that proves it. Eyes are amazing machines and very
sensitive but do most people take care of them? What do you think? Well nature's
done her best given us eyelids, eyelashes, built-in blinds and shutters, built-in
brooms and filters but we don't give her any help. Protection is what it's all
about. It's too late if something happens to them. Look you only get two eyes so
why not look after them? And television is one of the worst offenders. Well not
television itself but viewers. I'll show you what I mean. Now this is not the way
to watch TV. Not if you care about your eyes. Lying on the floor below the line
of the set too close to the screen. Everything dark in the room with a
glaring light from the television set leaping out at you. Very confusing for
the rods and combs. Ah that's better. When you watch TV sit up on a level with the
set at least two meters away from the screen and have a light on somewhere
else behind you. It's not perfect yet but it's better. And when you're watching TV
give yourself a rest every now and then. No not by flopping all over the floor to
rest your back and strain your eyes. Look away from the screen for a few seconds.
Would you like to try that now? I promise you I won't do anything exciting till
you get back. Beautiful beautiful brown eyes. Oh how are your eyes? Better? So are mine.
These TV lights can be very hard in the rods and cones. Of course TV isn't the
only culprit. Sure it's a good thing to read a lot but not in bed with a torch.
Sit up with a good light behind you. It'll rest your eyes as well as your mind.
Torches are finding a way through the bush not through Robertson Crusoe. And
what about the Sun? Well that good old Sun the main source of our light is the
worst offender. Well rather we are. Look our ancestors had very protruding
forehead and eyebrows like Sun visors built in. Well we've lost them over a
few thousand years. So if you're going out in the Sun wear a hat. Not only to
protect your skin but to protect your eyes. Great she's going to the beach. So
what she's forgotten? Neanderthal man may not have needed a hat. We do.
By the way I've even met some crazy people who need special glasses to help
their eyes. People have gone to all the trouble of getting the right glasses
made and then they don't even wear them. Now look do yourself and your eyes a
favor. Give them the help they need. Tell you what let's make a pact. If I wear my
glasses will you wear yours? The eclipse of the Sun in October 1976 reminded
people in Australia just how dangerous it is to look at the Sun at any time and
more especially during an eclipse. In spite of this some people did look at
the Sun and they suffered permanent eye damage. The only safe way to look at an
eclipse of the Sun is on film or on television. While this videotape was
being recorded even the cameraman had their eyes turned away from the eclipse.
How often have you said I know it's there because I've seen it myself? Well
mostly our eyes do tell us the truth but sometimes they play tricks on us. These
lines appear to be the same length. Do you agree? But what happens when we add
some tails to the lines going different ways?
Do the lines still look the same? And what about these? These lines are equal
and parallel. We're certain of that but add some more lines radiating outwards
and they don't look parallel anymore. They seem to bend outwards. Try it for
yourself later. Now does the trick happen on the page or in the retina or in the
brain? Watch the center of this whirling spiral. You may feel the center is moving
towards you and when it stops you may feel the center is moving away. Apart
from the tricks our eyes play on us we all see things in a different way. Is
this a picture of two faces or a candle? And depending on your mood of the moment
this could be a picture of two angry faces or a pattern of a cross and an
arrow. We all look at things but what we see depends on our own interest. If you
look at a suburb from some distance away it's just a suburb, a jumble of houses
but the whole thing means a lot more if one of those houses is your home. Then
you begin to notice things. You see more because you have a special interest.
Sight is one of the most precious of the five senses. It's our main way of
learning about the world and our eyes are always ready to see more, to look
more closely, more deeply into the world around us.